1. Field of the Invention
This invention relates to an angle of advance correction signal generator responsive to the effect of pinging in a controlled ignition internal combustion engine.
2. Description of the Prior Art and Related Patent Applications
In the course of developing a new gasoline engine, consideration of the pinging phenomenon has become a habitual phase of the motor mechanic's work. Precise experiments enable him to select a compression rate that yields a good compromise among the following parameters: lack of pinging, specific torque value, efficiency, choice of fuel, with consideration of the precision of the advance devices available to him. With advance-angle generation devices consisting of moving mechanic parts, the motor mechanic provides for an advance angle reaching maximum specific torque and/or with a ping clearance on the order of eight degrees. This limit can become disadvantageous in engines where the ping limit is close to or ahead of the optimum advance.
Various tests have shown that this clearance can be reduced by means of adding simple angle unkeying or decrementing devices such as switching according to the engine water temperature or the air temperature in the intake manifold, to means giving the ignition instant, for example by switching the signals delivered by a distributor with two electromagnetic pick-ups or with unkeyed Hall effect to give a translation of the advance system. However, these devices may be satisfactory for certain operating points but are ill-suited for the law of advance and do not make it possible to have an ignition point at the optimum moment for the engine. It is therefore appropriate to bring about unkeying only when this is necessary, and in order to make the engine work under optimum conditions. At present, the technician can design or utilize electronic ignitions with advance cartograpy preprogrammed according to the various values for engine rotation speeds and/or the vacuum in the intake manifold, and thus provide for an advance law closer to the engine's optimum efficiency values. It will be easy for him to adopt the device described hereinafter to unkey the ignition point so as not to cause pinging.
The most effective method for ping detection is analysis of the pressure in the engine's combustion chamber. This method requires expensive transducers. Therefore, a preferred approach involves an analysis of the vibrations of the engine's cylinder head by means of vibration transducers, for example of the seismic type. Analysis of the vibrations, both in frequency and amplitude, of half a revolution shows different phases of excitation, in particular the noise due to combustion and activation of the intake and exhaust values. The combustion phase starting at the moment of ignition only presents characteristic ping signal points in the vicinity of the engine's maximum pressure; therefore it is appropriate to examine the signal from the vibration pick-up throughout the maximum pressure phase.
Ordinarily, an angular window is created linked in rotation to the crankshaft and making it possible to record the signals relative to the combustion noise only at the time of this phase. The combustion noise is a function of the rotation speed, the angle of advance, the vacuum in the intake manifold, and the type of fuel used. Incorporating this noise into the angular window is a key element well known to the technician called on to deal with these subjects and makes it possible to increase the dynamics of the signal. The noise grows with the engine speed; incorporation of this noise for a varying period of time, inverse to the engine speed, reduces the interactions due to the variations in level caused by a variation in speed. Nonetheless, this solution is only sufficient for rather low engine speeds; subsequently the incorporated value increases with the engine speed; it is therefore necessary to work at a relative level by individualizing the values given for each cylinder.
A description of a ping detection system based on this principle will be found in commonly owned U.S. patent application Ser. No. 141,147 filed Apr. 17, 1980 for a "Process and System for Computation and Adjustment of now U.S. Pat. No. 4,300,503 Optimum Ignition Advance," which is hereby cross referenced.
In patent application Ser. No. 141,147, an initial process is disclosed calculating and adjusting the advance optimization of an internal combustion engine by means of a system for detection of pinging with the aid of a window such as an accelerometer rigidly attached to the engine's cylinder head characterized by the fact that the accelerometric signal is made to undergo an analog treatment including, in particular, integration of the signal inside a given window; conversion of the resulting signal into numerical form; calculation of an average value proportional to the preceding n pings; calculation of two thresholds of comparison S.sub.1 and S.sub.2, each of which is a linear function of the previously calculated average value; and comparison of the numerically incorporated accelerometric value to each of these thresholds, whereupon the existence or absence of a pre-pinging value and/or an audible ping value is deducted which is then used to act on the programmed electronic ignition advance.
Additionally, a system is there disclosed for calculating and adjusting the advance optimization of an internal combustion engine by means of a ping detection system consisting of a transducer such as an accelerometer rigidly attached to the engine's cylinder head, characterized by means for analog treatment of the signal picked up from the accelerometer 10, including in particular integrator logic circuits for controlling the integrator, an analogical-digital converter, and a microcomputer including in particular a sequencer, a stage for calculating an average value proportional to the preceding n pings, two stages for calculating comparision thresholds S.sub.1, S.sub.2, each of which is a linear function of the previously calculated average value, and circuits for deducing therefrom the existence or absence of a pre-ping value and/or audible pings.
The aforementioned patent application thus makes it possible to produce two detection thresholds, one called a pre-ping threshold and the other a ping threshold, detecting incorporated value levels greater than those of the pre-ping threshold.
Assuming that these prior signals have been demonstrated and are available, the present invention proposes a system for correcting the angle of advance capable of making use of the pre-ping and ping signals which have been brought to light by the process and system described in the aforementioned patent.